This invention relates generally to pumps, and in particular to a self-tightening retaining system for holding a cover in position closing an access port of a pump housing.
High pressure pumps are widely used in the petroleum industry for a variety of field operations relating to oil and gas wells. Such pumps deliver a fluid or slurry, which may carry solid particles (e.g., a sand proppant), at pressures up to 20,000 psi. A common type is a positive displacement pump having one or more plungers reciprocally movable in a corresponding pump chamber. Each chamber has an intake port for receiving fluid, a discharge port for exhaust, and a one-way flow valve in each port for preventing reverse flow. These valves require frequent maintenance. Components of the valves are formed of a material which forms an effective seal, such as polyurethane, but which is incapable of withstanding the erosive environment of the pump chamber for an extended duration. Typically, each valve must be serviced after every period of continuous operation at a well site (e.g., every four to six hours) for replacement of worn components. An access port is provided in a wall of the pump housing, at a location near the valves, so that maintenance personnel can readily reach the valves.
The access port must be securely closed and sealed for proper operation of the pump. A closure device, such as a plug with a circumferential seal, is provided for installation in the access port. A retaining cover is typically secured in the access port behind the closure to firmly hold the closure at its installed position. The retaining cover has external threads and is rotatably received in a threaded portion of the access port. Typically, a worker tightens the retaining cover in the access port to a high torque using a sledge hammer and a tool placed in a cavity of the cover to effect its rotation.
Unfortunately, the retaining cover is subject to inadvertently loosen. The pump experiences substantial vibration during operation at high power settings such that the retaining cover can overcome its initially applied torque and begin to “back out”, or rotate in the access port in a loosening direction. Should the retaining cover continue to loosen, the closure and a quantity of high pressure fluid would be ejected from the pump housing and potentially cause damage or injury. Consequently, safety regulations demand that operators respond to any loosening of the retaining cover by stopping the pump. That degrades efficiency and can necessitate the expense of back-up pump for continuing a pumping operation while the primary pump is shut down.